A. Field of the Invention
The device of the present invention relates to a new and improved tool for applying fasteners such as pierce nuts to a workpiece.
B. Description of the Prior Art
In the manufacturer of automobiles and similar vehicles, it is desirable to secure a fastener to the sheet metal such as employed in the body of the vehicle in a manner such that the fastener will not become loose due to vibration during the operation of the vehicle. In the prior art, a fastener such as a pierce nut is used to pierce an opening in the sheet metal and is then deformed to clinch the fastener in place on the sheet metal in the opening, thus simultaneously forming the opening, locating the nut properly over the opening and securing the fastener to the sheet metal.
Typically, the prior art tools employed to secure fasteners such as pierce nuts to sheet metal include a punch reciprocally mounted within a housing for engaging a strip of fasteners such as pierce nuts. The stroke of the punch is such that at a point during a stroke it engages one of the nuts on the strip, severes the nut from the strip and forces it into a nose assembly of the tool that is aligned with the workpiece. After a sufficient number of fasteners have accumulated into the nose assembly, the lower fastener is then forced into the workpiece by the punch's engagement with the next fastener in the fastener strip.
The feeding of the strip into the drive track of the prior art punch is accomplished by a feed plate. To operate the feed plate, a separate plunger is reciprocally mounted within the housing of the prior art tool and mechanically coupled to the punch so as to move simultaneously therewith. The separate plunger is coupled to the feed plate in a manner such that the vertical reciprocation of the second plunger imparts horizontal reciprocation to the feed plate. A separate feed pawl is connected to the feed plate and engages the fastener strip to advance the strip of fasteners. The plunger is coupled to the punch so as to be simultaneously reciprocated with the punch. If, however, at anytime the punch and plunger are moved out of parallel alignment with each other, binding will occur requiring adjustment or resulting in destruction of the tool. It has been typical with prior art tools of this type for the punch and plunger to become out of parallel alignment quite often during operation resulting in substantial costs and down time.
As is typical with tools of this type, there may be a jamming of fasteners in the drive track of the punch. If the tool is allowed to continue to operate, the punch will engage the jammed fasteners, thus destroying tool or parts thereof. Accordingly, it is desirable to prevent operation of the tool once jamming occurs. In one prior art tool this is accomplished through the employment of a strip stop member that is pivotally mounted in the housing of the tool and is biased into engagement with the punch. The strip stop member is moved out of the track of the punch upon engagement with a fastener being advanced into the drive track. After a fastener has been driven, if there is no jamming, the strip stop member pivots to its original position out of engagement with the punch, allowing the complete withdrawal of the punch. If there is an incomplete stroke of the punch or there is a jam in the feed track by a fastener, however, the strip stop member engages the fastener and cannot return to its original position. The strip stop member in this condition continues to engage the punch and prevents a complete withdrawal and further operation of the tool.
Examples of the typical prior art tools are described in U.S. Pat. Nos. 3,718,965; 3,811,171; 3,969,808; 3,969,809; and 3,971,116 and these patents are incorporated by reference for understanding the basic tool structure.
There are several different disadvantages with the typical prior art tools described. If a jam occurs, the operator of the tool can attempt to manually feed the nut strip into the tool since the feed path is not blocked which may damage the tool or result in injury to the operator. Also, the typical prior art tool requires several different parts. For example, the second plunger is necessary as are separate feed plate, pawl and strip stop member. This requires a large tool that is expensive to manufacture and assemble.
Another disadvantage of the typical prior art tool is that after a period of time, the punch becomes magnetized and fasteners tend to adhere to the punch through the magnetic effect. These fasteners are then pulled into a jamming position by the punch upon its retraction, resulting in damage to the tool.